1. Field of the Invention
The present invention relates to a heat sink, and more particularly, to a heat sink, a front side of which is picked and placed and surface-mounted and a rear side of which is reflow-soldered to a conductive pattern of a printed circuit board (PCB) by a solder paste.
In addition, the present invention relates to a small-sized heat sink capable of more efficiently diffusing and cooling heat generated from a heating element through a conductive pattern of a PCB disposed adjacent to the heating element, and also capable of being conveniently mounted on the conductive pattern at low costs.
2. Description of the Related Art
Recently, portable electronic communication devices such as a mobile phone have been reduced in size and weight while having increased in data processing speed and capacity. Accordingly, much heat is generated from a semiconductor chip that supplies main functions of the devices, which deteriorates the performances, for example a radio frequency (RF) performance of the semiconductor chip.
Also, a semiconductor chip such as a light emitting diode (LED) effecting high brightness generates much heat and the heat shortens the lifespan of the LED chip.
In general, a metal heat pipe having a high thermal conductivity, a heat sink, a polymer thermal pad and the like are used to effectively cool heat of a heating element or a heating module of a semiconductor, such as a field effect transistor (FET) mounted on a conductive pattern of a printed circuit board (PCB).
Additionally, for efficient cooling of heat, thermally conductive ceramic or metal may be used for the material of a PCB in a light emitting diode (LED) lighting device which generates much heat. In this case, a part performing cooling in the ceramic or metal circuit board requires a uniform thickness, a complicated process, and a high cost. For example, if the whole circuit board is made of a high-thermal-conductivity material for cooling of the heating element, an expensive material is used even for a part insusceptible to heat, accordingly increasing the material cost.
General heat sinks are manufactured by processing a high thermal-conductive metal such as Al with various methods including die-casting, powder injection molding (PIM), and casting, and mounting the processed metal on a heating element. Therefore, heat of a heating part is transferred to the heat sink and radiated and diffused to the air through the heat sink. To this end, an exemplary heat sink has a wide area for contact with the heating element, a wide outer surface for contact with air, a high thermal conductivity, and a high thermal diffusion efficiency.
For this purpose, according to a related art, a heat sink made of metal such as Al is formed to have predetermined volume and shape having a horizontal rear side and a wide-area front side for contact with air. The metal heat sink is attached on a heating element mounted on a PCB using an adhesive made of any one of thermally conductive elastic rubber, a pad, and an adhesive tape.
However, when the heat sink is mounted using such elastic adhesive, pad, or adhesive tape, an adhesion strength and a thermal conductivity are reduced compared to the case of using a soldering method. Also, according to the related art, mounting of the heat sink is hard to automate and therefore is manually performed. Accordingly, the mounting cost is increased while reliability of the product and convenience of rework are reduced.
In other words, it is difficult to apply a pick-and-place method and a surface mounting technology (SMT) by reflow soldering with a solder paste to the heat sink.
Furthermore, the related-art heat sink is large and heavy. Especially in a personal terminal device such as a mobile phone and a personal digital assistant (PDA) restricted in size and weight, the large and heavy heat sink is limited to be applied.
Especially, in a small device such as the personal terminal device, it is difficult to secure height for mounting the heat sink on a heating element.
In addition, when an insulation coating process to prevent corrosion, such as anodizing, is performed with respect to the heat sink made of Al, the thermal conductivity is reduced.
In addition, the mounting position of the related-art heat sink is usually limited to a position on the heating element.
Also, being mounted on the heating element, the related-art heat sink merely radiates and diffuses heat but is not expected to increase an electrical ground area on the conductive pattern in the PCB.
Furthermore, the related-art heat sink is incapable of cooling a specific electrical contact terminal which is especially susceptible to heat, more than a plurality of other electrical contact terminals mounted on the heating element. Furthermore, the related-art heat sink costs a lot.
Meanwhile, in the case where the heating element is a semiconductor part constituted by a bare chip, a lead frame which connects the bare chip to an electrical circuit of a PCB, and an epoxy molding compound (EMC) which protects the bare chip and the lead frame, the EMC having a low thermal conductivity is ineffective to radiate and diffuse heat of the bare chip to the outside through a heat sink mounted thereon.
Heat of the heating element can be efficiently removed by increasing the volume of a heat sink, using a high-thermal-conductivity material, and improving the structure of a heat sink or a heat pipe and the adhesion method. However, the related-art technology is insufficient to effectively remove heat of a heating element equipped in a relatively small terminal device.